1. Field of the Invention
The present invention relates to resistance substrates and variable resistors, and more specifically, to a resistance substrate having a variable resistance between two conductive elements and a variable resistor including a slider which slides along a resistor element provided on a substrate member to adjust a resistance.
2. Description of the Related Art
A rotary variable resistor including a slider which slides along a resistor element to adjust a resistance is disclosed in Japanese Unexamined Patent Application Publication No. 2003-124009. FIG. 8 shows a manufacturing step of this variable resistor, in which a substrate member 10 is formed on a hoop material 40 by resin molding, the hoop material 40 being formed into a shape corresponding to terminals by a punching process. FIG. 9 shows a state in which a substantially annular resistor element 15 is formed on the substrate member 10 and metal terminals 12 and 13 are separated from the hoop material 40.
The terminal 12 includes terminal portions 12a and an annular current collector 12b, and the current collector 12b is exposed on the surface of the substrate member 10. In addition, a pair of terminals 13 includes terminal portions 13a and end portions 13b, and the end portions 13b are exposed on the surface of the substrate member 10. The current collector 12b and the resistor element 15 are concentric with respect to each other, and a slider (not shown) slides along the current collector 12b and the resistor element 15, such that a resistance between the terminals 12 and 13 is adjusted depending upon the rotation angle of the slider.
The resistance obtained when the slider is rotated to a maximum rotation angle is proportional to the length of the resistor element 15 between the end portions 13b, and a variable resistance range corresponds to the length of the resistor element 15 excluding an area corresponding to an angle Y between the end portions 13b. The angle Y refers to a maximum angle between lines extending from the center of the resistor element 15 through the end portions 13b. That is, an angle between lines extending through the outermost positions of the end portions 13b. 
In this variable resistor, the pair of terminals 13 are obtained by forming the hoop material 40 into a corresponding shape by the punching process using a mold. Therefore, when various types of variable resistors having different variable resistance ranges are to be manufactured, the same number molds as the number of types of variable resistors must be provided to form the end portions 13b at different positions (that is, to obtain different angles Y). However, this is not practical since it is difficult, time consuming and expensive to design and produce multiple types of molds. This problem is not limited to rotary variable resistors, and variable resistors having linearly-moving sliders also have a similar problem.
In addition, in rotary variable resistors, it is necessary to arrange the end portions 13b as close as possible to each other (that is, to make the angle Y as small as possible) to increase the variable resistance range. However, since the terminal 12 having the current collector 12b integrated therewith is located between the terminals 13, the terminal 12 prevents the end portions 13b from being arranged very close to each other. Therefore, there is a limit on the amount that the variable resistance range can be increased.